The following processes all have some problems, which may be diagnosed by careful observation of the PID controller’s faceplate display (PV, SP, and Output values) and/or indications given by gauges in the field.
Examine each control system and determine the loop faults in each one from the information given.
Assume that the conditions shown have existed for quite some time (long enough for the control system to have brought the process variable back to setpoint if everything were operating correctly):
1. Solar Panel Temperature Loop
2. Level Loop
3. Heat Exchanger Loop
A valuable principle to apply in a diagnostic scenario such as this is the correspondence: identifying which values agree with each other. Explain how a check of correspondence tells us which instrument is at fault in any of these control loops.
For each of these scenarios, determine what your next diagnostic test might be to further pinpoint the location and nature of the problem.
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Credits: Tony R. Kuphaldt